This invention relates generally to the control of pneumatic tire fabrication and more particularly to the control of the bladder shaping pressure in a pneumatic tire molding press.
While pneumatic tires are being loaded into a tire molding press and while they are being molded in the press, the tire is internally supported on an inflatable bladder. The control of the fluid pressure in the bladder is particularly critical while the tire is being loaded into the tire press and the tire press is closing onto the tire (this is commonly called the shaping pressure).
Heretofore, the shaping pressure has been controlled by manually adjusted pressure regulators that theoretically set each shaping pressure to which the tire is to be subjected during loading. Typically, two such shaping pressures are used, a "hold shape" pressure that holds the tire in position while the loaders are being retracted and a "first shape" pressure that holds the tire in position while the tire mold is being closed onto the tire. Once the tire mold is closed, a different set of pressures and operating conditions are applied while the tire is being cured. One of the problems associated with such prior art control schema is that a separate pressure regulator is usually required for each pressure selected. Moreover, adjustments in the particular pressure settings to compensate for different conditions such as high temperature, a delay causing the press to remain open too long, a delay in the loading of the tire mold, or a new bladder being installed on the tire mold, was difficult to achieve without elaborate valve and relay systems. This caused such prior art control systems to be difficult to set up and operate and to be costly. Further, the ability of such manually adjusted pressure regulator to maintain substantially constant pressure setting is limited due partly to the response time in making corrections and due to the accuracy of the pressure regulators themselves. As a result, difficulties have been encountered with the use of such prior art systems. One difficulty is an unacceptably high scrap loss due to improperly made tires and another difficulty is lower production yields in the operation of the tire molding presses.